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Ultrasonography |
1 Departments of Radiology (M.A.B., J.P.H., G.C., B.B.G.)
2 Surgery (D.B.H.), University of California, San Diego, 200 W Arbor Dr, San Diego, CA 92103-8756.
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Abstract |
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MATERIALS AND METHODS: Reports of all abdominal US examinations performed at one institution for blunt trauma from October 1995 through June 1996 were reviewed. The charts of patients with intravascular gas were examined to determine the mechanism of injury, associated findings, and clinical outcome.
RESULTS: A total of 730 patients underwent abdominal US examinations during the 9 months of study; five had intravascular gas demonstrated. Two patients had portal venous gas, one had hepatic venous gas, and two had inferior vena caval gas. Four of the five patients were involved in motor vehicle accidents, and one had been assaulted. In patients in whom follow-up studies were obtained, there was no evidence of intravascular gas at US or computed tomography. No cause was found at imaging or clinical examination.
CONCLUSION: Intravascular gas may occur as a transient incidental finding after blunt abdominal trauma.
Index terms: Abdomen, injuries, 70.40 • Abdomen, US, 70.1298, 70.40 • Hepatic veins, 982.499 • Hepatic veins, US, 95.1298, 95.40 • Portal vein, gas, 957.499 • Portal vein, US, 957.1298 • Venae cavae, abnormalities, 982.499 • Venae cavae, US, 982.1298, 982.499
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Introduction |
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MATERIALS AND METHODS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Patient Selection
All patients with a mechanism for blunt abdominal trauma requiring activation of the trauma team during this period were candidates for US evaluation. After initial evaluation by a trauma surgeon, those patients suspected of having blunt abdominal injury who did not require immediate laparotomy were eligible for US to identify fluid in the peritoneal cavity and also to identify visceral abnormalities. After US, computed tomography (CT) was performed if the US findings were abnormal or if CT was requested by the evaluating surgeon.
Technique
All US examinations were performed in the resuscitation suite by registered diagnostic medical sonographers by using either a model HDI 3000 (Advanced Technology Laboratories, Bothell, Wash) or a model 128-XP (Acuson, Mountain View, Calif) machine. In most cases, a 3.5-MHz sector probe was used, although, when indicated for better imaging, a 2.25- or 5.0-MHz sector probe or a 5.0-MHz curved array probe was used. Duplex studies were not routinely obtained, unless there was a vascular indication; all US equipment used had Doppler capabilities. Examinations were recorded with the Image Link system (Eastman Kodak, Rochester, NY) for subsequent evaluation by radiologists. The seven routinely evaluated areas included the left and right upper quadrants, the epigastrium, the paracolic gutters, the retroperitoneum, and the pelvis. Attention was directed to the presence of free fluid and the gross appearance of the heart and abdominal organs. Vessels were not specifically evaluated as part of the abbreviated abdominal examination for trauma. If a vascular abnormality was detected by the sonographer or radiologist, attention was directed to the abnormality, and attempt was made to document the finding.
Intravascular gas was identified as small mobile echogenic foci moving quickly in the direction of blood flow within a vessel. Gas was distinguished from other particulate matter by its intense echogenicity and a velocity greater than that expected for blood within the vessel. The diagnosis was based on the real-time appearance. When this finding was encountered, a segment of the real-time examination was recorded on videotape and a duplex study was obtained in addition to the routine recording of static images on film. Follow-up imaging was performed at the discretion of the trauma surgeon.
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RESULTS |
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DISCUSSION |
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Systemic venous gas has been associated with iatrogenic causes, decompression sickness, and penetrating trauma; few cases of spontaneous occurrence have been described. Systemic venous gas has been seen with intestinal pneumatosis in a patient with known portal hypertension (14). Three cases of concurrent portal and systemic venous gas have been reported, each suggesting a different mechanism of passage of gas between the systemic and portal systems (15,16). The possible mechanisms include recent surgery, portosystemic shunt due to portal hypertension, and passage of gas via hepatic sinusoids. To our knowledge, systemic venous gas due to blunt trauma has not been reported on.
Our experience suggests that intravascular gas occurs in less than 1% of patients with blunt abdominal trauma. This may be an underestimation of the true incidence, because abdominal vessels were not routinely examined as part of our trauma US protocol. Thus, the five patients described had intravascular gas diagnosed incidentally, and more cases may have gone unrecognized. We have not observed benign intravascular gas in patients without trauma in our regular US practice. For this reason, we believe the relationship is causal, although a control group of young patients without trauma was not examined.
In the four patients in whom follow-up studies were obtained, the finding had resolved, while the fifth patient had no sequelae at clinical follow-up. The most likely mechanism, which has been postulated previously, is that of sudden increase in intraabdominal pressure caused by the impact, which forces intraluminal gas into the bowel wall, where it is absorbed into the portal circulation. Once in the portal system, the gas may pass into the hepatic veins via sinusoids. Gas in the inferior vena cava may arise from sites of portosystemic communication. No patient underwent placement of femoral catheters, and, although femoral arterial punctures are routine for blood gas analysis, it is unlikely that accidental venipuncture caused the quantity of gas observed in the inferior vena cava. At our institution, US is typically performed within 20 minutes of patient arrival (17). This may explain why our detection of transient intravascular gas was more frequent than that previously described with CT, which requires transportation and longer delay in many circumstances.
The interest in US for the examination of patients with blunt abdominal trauma has been rapidly increasing, especially in the surgery literature. Several reports now support the utility and flexibility of US in this setting (17–23). Reports vary as to who performs and interprets the study and the detail of the examination. At our institution, US is performed by registered sonographers by using state-of-the-art equipment with Doppler capabilities. The studies are interpreted by both radiologists and trauma surgeons concomitantly. The examination is an abbreviated abdominal study; however, it is more detailed than the focused abdominal sonography [US] for trauma, or FAST, examination in use at other institutions. In that examination, the right and left upper quadrants and the pelvis are imaged only for free fluid. Up to 29% of abdominal injuries may be missed by using this technique (23). In addition to parenchymal defects, intravascular gas would probably not be recognized by using the focused abdominal US for trauma technique, and this may help explain the absence of this finding in the existing trauma US literature.
As the use of US in the initial examination of patients who have had trauma increases, along with the experience of those using the technology, intravascular gas will likely be encountered more frequently. Additional findings may prompt further imaging or treatment; however, intravascular gas after blunt abdominal trauma can occur without associated abnormalities or disease. It should therefore be recognized as a possibly benign finding, and emphasis should be placed on clinical judgment to determine therapy and follow-up.
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Footnotes |
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From the 1997 RSNA scientific assembly.
Author contributions: Guarantor of integrity of entire study, G.C.; study concepts and design, G.C.; definition of intellectual content, G.C.; literature research, M.A.B., J.P.H.; data acquisition and analysis, M.A.B.; manuscript preparation, M.A.B., J.P.H.; manuscript editing, G.C., B.B.G., D.B.H.; manuscript review, G.C.
Received February 26, 1998;
revision requested May 5, 1998; revision received July 27, 1998;
accepted September 28, 1998.
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